Pressure Converter
Convert pressure between PSI (UK tyre pressure), bar (European standard), kilopascals, atmospheres, mmHg (blood pressure), and pascals. Enter a value in any unit to see all conversions instantly.
Reviewed by Richard Ross · Last updated April 2026
How Pressure Converter works
Common pressure units
PSI (pounds per square inch) is used for tyre pressure in the UK and US. Bar is common in European automotive and industrial contexts. kPa (kilopascal) is the SI-preferred unit. 1 bar = 100 kPa ≈ 14.5 PSI.
Quick reference conversions
Common conversions: 30 PSI = 2.07 bar = 206.8 kPa. 32 PSI = 2.21 bar = 220.6 kPa. 35 PSI = 2.41 bar = 241.3 kPa. 2.5 bar = 36.3 PSI = 250 kPa. 1 atm = 14.696 PSI = 1.013 bar = 101.325 kPa = 760 mmHg. For tyre pressure: multiply bar by 14.5 to get PSI, or divide PSI by 14.5 to get bar.
Standard atmosphere
1 atmosphere (atm) = 101.325 kPa = 1.01325 bar = 14.696 PSI. This is the average air pressure at sea level. Atmospheric pressure varies with weather and altitude — at the summit of Ben Nevis (1,345m), atmospheric pressure is approximately 860 hPa, about 15% lower than at sea level.
Blood pressure (mmHg)
Blood pressure is measured in millimetres of mercury (mmHg). A reading of 120/80 mmHg is considered normal. 1 mmHg = 133.322 Pa.
Tyre pressure in the UK
UK vehicle manufacturers specify tyre pressure in PSI on the tyre placard inside the driver's door or in the handbook. Continental Europe uses bar on tyre pressure gauges at petrol stations. Most UK forecourt gauges show both. Typical car tyres run at 28–36 PSI (1.9–2.5 bar) cold. Under-inflation by even 5 PSI (0.34 bar) increases rolling resistance and tyre wear, and can reduce fuel economy by 1–2%.
Industrial and engineering applications
In UK engineering and manufacturing, pressure is commonly expressed in bar (process industries), PSI (hydraulics, pneumatics), and kPa or MPa (structural and civil engineering). Boiler pressures are typically 1–10 bar. Hydraulic systems in construction machinery operate at 200–350 bar (2,900–5,000 PSI). Scuba diving cylinders are filled to around 200–300 bar (2,900–4,350 PSI).
Weather and atmospheric pressure
Atmospheric pressure is measured in hectopascals (hPa) or millibars (mbar) in meteorology — these are identical units (1 hPa = 1 mbar = 100 Pa). Standard sea-level pressure is 1,013.25 hPa. UK weather forecasts describe high pressure (anticyclones, typically 1,020–1,050 hPa, associated with settled weather) and low pressure (depressions, below 1,000 hPa, associated with rain and wind). The UK record low was 925.5 hPa during the January 1884 storm.
Frequently asked questions
What is the tyre pressure in PSI vs bar?
Most UK cars recommend 30–35 PSI (2.07–2.41 bar). The tyre placard on the driver's door shows the manufacturer's recommended pressure in both PSI and bar.
How many PSI in 1 bar?
1 bar = 14.5038 PSI.
What is normal atmospheric pressure in kPa?
Standard atmosphere = 101.325 kPa.
What is a normal blood pressure in kPa?
Normal blood pressure is 120/80 mmHg = 16.0/10.7 kPa. Blood pressure is almost universally expressed in mmHg rather than SI units.
How do I check my tyre pressure in the UK?
Use a tyre pressure gauge (digital or analogue) or the machine at a petrol station forecourt. Check the pressure when the tyres are cold (driven less than 2 miles). Find the recommended pressure on the sticker inside the driver's door jamb or in the vehicle handbook. Both PSI and bar are usually shown.
What is the difference between gauge pressure and absolute pressure?
Gauge pressure measures pressure relative to atmospheric pressure (so a flat tyre reads 0 PSI gauge, not 14.7 PSI). Absolute pressure adds atmospheric pressure on top. Tyre gauges read gauge pressure. Scientific instruments and some industrial applications use absolute pressure. The suffix "g" (psig) or "a" (psia) indicates which scale is being used.
What is the conversion formula between PSI and bar?
1 PSI = 0.0689476 bar. To convert PSI to bar, multiply by 0.0689476. To convert bar to PSI, multiply by 14.5038. For a quick mental estimate: divide PSI by 15 to get approximate bar (e.g., 30 PSI ≈ 2 bar).
What pressure unit does the NHS use for blood pressure?
Blood pressure is measured in mmHg (millimetres of mercury) worldwide. A normal reading is 120/80 mmHg. This equals 16.0/10.7 kPa or 2.32/1.55 PSI. The mmHg convention persists from when blood pressure was measured using mercury manometers, even though modern devices are digital.
What pressure should bicycle tyres be?
Road bike tyres: typically 80-130 PSI (5.5-9.0 bar). Mountain bike tyres: 30-50 PSI (2.1-3.4 bar). Hybrid/commuter tyres: 50-70 PSI (3.4-4.8 bar). The correct pressure depends on tyre width, rider weight, and terrain. Check the minimum and maximum range printed on the tyre sidewall.
Why do European tyre gauges use bar instead of PSI?
Continental Europe and most of the world adopted metric units, making bar (and kPa) the standard for tyre pressure. The UK, US, and some Commonwealth countries still commonly use PSI. Most UK petrol station tyre inflators show both PSI and bar. Vehicle handbooks for cars sold in the UK typically list both units.